JP4923364B2 - Reactive gas generator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gas generating apparatus that generates a low temperature plasma in a high pressure state by adjoining a processing chamber for processing an object to be processed and a low temperature plasma generation unit, and a gas generation method using the same, The present invention relates to a gas generator for performing water and sewage treatment, decontamination treatment of contaminated water, and hazardous substance treatment, and a method for generating the same.
[0002]
[Prior art]
Conventionally, chemical treatment of gas, detoxification of contaminated water, treatment of hazardous substances and waste, development of new materials including surface treatment, reaction treatment and reaction promotion in resist peeling and oxide film formation in semiconductor manufacturing processes As a means, a discharge plasma method is used.
The method of using discharge plasma is to use thermal plasma (for example, arc discharge) by heat generated from discharge, and to generate high-energy electrons and to use collisional dissociation between electrons and matter rather than heat from discharge. There is a way. In particular, the latter is called thermal non-equilibrium discharge plasma (hereinafter referred to as low temperature plasma) having a high electron temperature (electron energy) and a low gas temperature (energy of neutral particles and various ions). Generated by discharge, electron beam irradiation, and the like. The target field is distinguished by the type of gas introduced into the discharge plasma, and can be an effective means for promoting chemical reaction with ionization of gas generated at low temperature and various radicals.
Examples of utilizing low-temperature plasma include detoxification treatment of waste water and wastewater and industrial oxidation treatment that generate and use active oxygen species and radical species. Ozone, which is one of the active oxygen species, has a longer life than other active oxygen species and is characterized by having strong oxidation properties next to fluorine in nature. Used.
In the conventional water and sewage treatment, for example, a downward injection type multi-stage ozone contact layer described in JP-A-8-243572 and a control method thereof (hereinafter referred to as disclosed example 1) are described. Hereinafter, it will be briefly described with reference to the drawings.
In FIG. 9, 40 is an ozone contact tank, 41 is an inflow pipe, 42 is an ozone gas injection part, 43 is an ozone generator, 44 is water to be treated, 45 is an ozone gas introduction pipe, and 46 is exhaust ozone gas.
In the above configuration, the ozone generator 43 generates ozone gas, which is a reaction gas used for water treatment, and the ozone gas is sent to the ozone gas injection unit 42 through the ozone gas introduction pipe 45, and is covered at the orifice of the ozone gas injection unit. The ozone gas is dissolved in the treated water 44, introduced into the ozone contact tank 40 through the inflow pipe 41, and the ozone gas not used for the treatment is discharged as exhaust ozone gas 46. In the configuration as described above, the ozone gas can be dissolved in the water to be treated relatively efficiently in the orifice portion, and the reaction between the ozone gas and the water to be treated is provided by providing the ozone contact tank in the subsequent stage. Water treatment efficiency is improved by making the time (also referred to as residence time) relatively long.
Similarly, as a method using active oxygen species and radical species, Japanese Patent Laid-Open No. 5-319807 (hereinafter referred to as “Disclosure Example 2”) directly inserts a high voltage application electrode into a water tank to be treated, Air or oxygen is generated as fine bubbles from a large number of hollow fiber membranes having pores, and discharge is generated in the bubbles to generate active oxygen species and perform water treatment (FIG. 10).
[0003]
[Problems to be solved by the invention]
The conventional gas generating apparatus generates active oxygen species and radical species by the discharge plasma method as shown in the first and second disclosed examples, and performs reaction treatment with the object to be treated by various methods.
However, in the above disclosed disclosure example 1, the generated ozone gas itself is unstable, and the contact portion (ozone gas injection portion) between the ozone generation unit (ozone generation device) and the water to be treated is completely separated. For this reason, the utilization rate of ozone gas generated by pressurization, transportation to an ozone gas injection part, contact with the wall surface of ozone gas generated during dissolution in water, decomposition by heat, or the like was low. Dissolution of ozone gas utilizes the differential pressure generated at the orifice portion, so the efficiency of ozone gas dissolution is not always sufficient, and there is a problem that a large amount of exhaust ozone gas that has not contributed to the treatment is generated. Due to the relatively long ozone gas introduction pipe, there was a time delay from the ozone generator to dissolution with the water to be treated, and active oxygen species other than ozone could not be used. In addition, a large-scale ozone contact tank is required to obtain a sufficient treatment reaction.
In the above-mentioned disclosed example 2, there is a problem that the electrode surface is corroded because the electrode is constantly exposed to the generated highly oxidizing substances (such as ozone and OH radicals) when immersed in water. There was a problem in terms of life. In addition, since water plays the role of a capacitor with a high relative dielectric constant, much of the energy input between the electrodes is used to increase the temperature of the liquid layer as Joule heat, resulting in high power efficiency and stable activity. It was difficult to ensure the production performance of oxygen species.
Accordingly, the present invention has been made in consideration of the above points, and is a reactive gas that is small in size, high in energy efficiency, can obtain a stable discharge, and can effectively use the generated active oxygen species and radical species. An object is to provide a generator.
[0004]
In order to solve the above problem , according to one aspect of the present invention, a pulse power source that generates a pulse high voltage having a voltage waveform with a steep rise, a source gas introduction portion made of oxygen or air, and a high voltage electrode And a low voltage electrode are opposed to each other through a predetermined discharge space, and the pulse high voltage is applied between the high voltage electrode and the low voltage electrode to form a streamer discharge in the discharge space. A reactor that generates a reactive gas containing radical species from the source gas by plasma, and a nozzle portion having a smaller cross-sectional area than the introduction portion, and the reactive gas is taken out from the reactor through the nozzle portion An extraction portion, wherein the source gas is introduced so that the pressure in the discharge space is higher than the pressure in the vicinity of atmospheric pressure, and the reactive gas is supplied from the nozzle portion at a high speed. Configured reactive gas generator to output is applied.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a cross-sectional view of a gas generator using low-temperature plasma generated under high pressure according to the present invention. In the figure, the same reference numerals are used for common parts, 10 is a reactor, 14 high-voltage electrodes, 15 low-voltage electrodes, 16a and 16b dielectrics, 19 source gas introduction parts, and 20 It consists of a reactive gas take-out part and 21 nozzle parts. 11 is a processing chamber for reacting with an object to be processed, 12 is a raw material gas for generating a reactive gas, 13 is a reactive gas generated by low temperature plasma, 17 is a low temperature plasma, and 18 is a pulse power source. It is.
Next, the operation of this apparatus will be described with reference to FIG. When the raw material gas 12 is introduced into the reactor 10 from the introduction unit 19 under a pressure higher than that of the treatment chamber 11 where the object to be treated is arranged, the boundary between the extraction unit 20 of the reactive gas 13 and the treatment chamber Since the gas flow is hindered in the vicinity, a pressure higher than that in the processing chamber is generated inside the reactor. Under this state, when a pulse high voltage is applied from the pulse power supply 18 between the high voltage electrode 14 and the low voltage electrode 15 disposed in the vicinity of the extraction portion, the neutral particle density increases with the increase in gas pressure, and the high pressure Discharge is formed and high-density low-temperature plasma 17 is generated. The high-density low-temperature plasma generates the high-density reactive gas containing active oxygen species and radical species. The reactive gas is immediately sent into the processing chamber using the pressure difference between the processing chamber adjacent to the vicinity of the extraction portion, and the processing reaction is performed by contacting the object to be processed.
Next, an example of a gas generator to which the above operation is applied is shown.
(First embodiment)
FIG. 1 is a cross-sectional view of a gas generator showing a first embodiment of the present invention. A high voltage electrode 14 and a low voltage electrode 15 are arranged in opposition to each other in the vicinity of the extraction portion 20 for the reactive gas 13 with a predetermined gap length. By making the high-voltage electrode an uneven surface instead of a smooth surface, a strong electrolysis field can be formed at the tip of the projection, high-energy electrons can be generated, and the pressure rise in the low-temperature plasma 17 generating portion Accordingly, it is possible to make the generation of discharge in a high density state relatively easy.
(Second embodiment)
FIG. 2 is a cross-sectional view of a gas generator showing a second embodiment of the present invention. A high voltage electrode 14 and a low voltage electrode 15 covered with a dielectric 16b are arranged in opposition to each other in the vicinity of the extraction portion 20 for the reactive gas 13 with a predetermined gap length. By covering the surface of the low voltage electrode and the vicinity thereof with a dielectric, only low temperature plasma can be formed without generating thermal plasma such as arc discharge at the time of discharge in a high density state. In addition, by making the high-voltage electrode a rough surface instead of a smooth surface as in Example 1 described above, it is possible to generate high-energy electrons that contribute to the treatment reaction, and it is relatively easy to generate discharge. can do.
(Third example)
FIG. 3 is a cross-sectional view of a gas generator showing a third embodiment of the present invention. A high-voltage electrode 14 covered with a dielectric 16a and a low-voltage electrode 15 covered with a dielectric 16b are disposed in the vicinity of the reactive gas 13 extraction portion 20 via a predetermined gap length. Since the high-voltage electrode and the low-voltage electrode are each covered with a dielectric, the electrode surface is prevented from being sputtered by the high-density low-temperature plasma 17, and the corrosion of the electrode by the generated reactive gas is prevented, thereby extending the electrode life. Can do. In addition, it is possible to suppress instability of discharge due to discharge scrap and transition to arc discharge, and to perform clean high-density low-temperature plasma processing.
(Fourth embodiment)
FIG. 4 is a sectional view of a gas generator showing a fourth embodiment of the present invention. A nozzle portion 21 is provided in the extraction portion of the reactive gas 13, and a high voltage electrode 14 covered with a dielectric 16a and a low voltage electrode 15 covered with a dielectric 16b are provided in the vicinity of the nozzle portion via a predetermined gap length. Are opposed to each other. Since the inside of the reactor 10 can maintain a stable pressure regardless of minute pressure fluctuations in the processing chamber 11 by the nozzle portion, the low temperature plasma 17 can be generated relatively stably. Since the reactive gas can be ejected at a high speed by the nozzle part, it is possible to obtain a high dissolution efficiency with the object to be processed and also to perform partial local processing. In addition, since the high voltage electrode and the low voltage electrode are each covered with a dielectric, the same corrosion prevention as in Example 3, prevention of discharge instability and transition to arc discharge, clean high density Low temperature plasma processing is possible.
(5th Example)
FIG. 5 is a sectional view of a gas generator showing a fifth embodiment of the present invention. The surface of the high voltage electrode 14 of the low temperature plasma 17 generating portion is formed in an uneven shape, and is arranged in a coaxial cylindrical shape with an appropriate gap length maintained on the central axis of the low voltage electrode 15. As in Example 1 described above, a strong electrolysis field can be formed at the tip of the protrusion, so that high-energy electrons contributing to the treatment can be generated, and as the pressure in the low-temperature plasma 17 generation section increases, It is possible to relatively easily generate a discharge in a density state. In addition, the coaxial gas cylindrical structure ensures that the source gas 12 always passes through the low temperature plasma 17 and the structure of the reactor 10 can be facilitated.
(Sixth embodiment)
FIG. 6 is a sectional view of a gas generator showing a sixth embodiment of the present invention. A rod-like or linear high-voltage electrode 14 covered with a dielectric 16a is arranged in a coaxial cylindrical shape with an appropriate gap length maintained on the central axis of the low-voltage electrode 15 covered with a dielectric 16b. . As in the third embodiment, sputtering of the electrode surface by the high-density low-temperature plasma 17 and corrosion of the electrode by the generated reactive gas can be prevented, and the electrode life can be extended. In addition, it is possible to suppress instability of discharge due to discharge scrap and transition to arc discharge, and to perform clean high-density low-temperature plasma processing. In addition, the configuration of the reactor 10 can be facilitated while the source gas 12 always passes through the low-temperature plasma by being configured in the same coaxial cylindrical shape as in the fifth embodiment.
(Seventh embodiment)
FIG. 7 is a sectional view of a gas generator showing a seventh embodiment of the present invention. A state in which a nozzle portion 21 is provided in the extraction portion 20 of the reactive gas 13 and the surface of the high voltage electrode 14 is formed in an uneven shape in the vicinity of the nozzle portion so that an appropriate gap length is maintained on the central axis of the low voltage electrode 15 Are arranged in a coaxial cylinder.
Similar to Example 4 described above, the nozzle unit can maintain a relatively stable pressure in the reactor 10 and can generate the low-temperature plasma 17 relatively stably. Further, the reactive gas can be ejected at high speed by the nozzle part, so that the dissolution efficiency with the object to be treated can be improved and partial local treatment can be performed. By making the surface of the high-voltage electrode uneven, it is possible to easily generate a discharge accompanying an increase in the pressure of the low-temperature plasma 17 generation part as in Example 1 described above, and to form the raw material gas 12 by configuring it as a coaxial cylinder. Can always pass through the low-temperature plasma, and the structure of the reactor can be facilitated.
The discharge electrode composed of the high-voltage electrode 14 and the low-voltage electrode 15 of the gas generator shown in FIGS. 1 to 7 is held at an appropriate gap length in the low-temperature plasma 17 generator and is arranged in parallel. The dielectrics 16a and 16b may be used irrespective of the presence or absence of the embodiment when the purpose is to prevent corrosion of the electrodes.
The shape of the low temperature plasma 17 generating part of the high voltage electrode 14 and the low voltage electrode 15 can be any combination of a planar shape and a protrusion shape, and the protrusion shape is a grooved uneven shape, a spiral protrusion shape, a concentric protrusion shape, As long as the structure can form an uneven electric field, such as a wire, rod shape, mesh shape, needle shape, or the like that has an uneven surface formed on the electrode surface such as a wire, the scope of the present invention is not deviated. If it is a shape, the shape is not ask | required.
When the shape having the nozzle portion 21 is used, the inside of the reactor 10 has a small cross-sectional area in the direction perpendicular to the flow direction of the raw material gas from the introduction portion 19 of the raw material gas 12 to the extraction portion 20 of the reactive gas 13. It is good also as a structure where the whole ventilation path is pressurized. In addition, regardless of the presence or absence of the nozzle part, the number of the introduction part and the extraction part does not need to be one, and the low temperature plasma 14 generation part has a pressure higher than atmospheric pressure or higher than the atmospheric pressure of the object to be processed. The shape is not limited as long as it can be formed.
Depending on the nature of the reactive gas 13 generated, a cooling structure is provided for the high-voltage electrode 14 and the low-voltage electrode 15 to generate the low-temperature plasma 14 generation part and the part until the reaction with the object to be processed is performed. The thermal decomposition of the reactive gas, the suppression of the explosion associated with the temperature increase of the reactive gas generated by the low-temperature plasma in a high density state, and the improvement of the generation efficiency of the reactive gas it can.
The extraction part 20 or the nozzle part 21 for the reactive gas 13 may be provided with a structure provided with a mechanism for preventing the backflow of the object to be processed into the reactor 10.
Next, an application example of a voltage applied from the pulse power supply 18 using the gas generator of FIGS. 1 to 7 configured as described above will be described with reference to FIG.
In either case of FIG. 1 to FIG. 7, a unipolar or high-polarity pulse high voltage can be used, and a streamer discharge, which is a filamentous discharge, is formed as a form of generation of low-temperature plasma 17, and a pressure near atmospheric pressure. The reactive gas 13 can be generated under higher pressure. When the pulse high voltage of extremely short unipolar or bipolar polarity with a rise time 31 of several ns to several tens of ns is used, electrons that have once lost their energy in collision with gas molecules are sufficiently accelerated again until the next collision. Therefore, the dissociation efficiency of gas molecules can be increased even under high pressure, and high-energy electrons can be generated with the pulse high voltage that rises quickly. Can be achieved. Depending on the target reactive gas, for example, ozone is a three-body structure consisting of a reaction (dissociation reaction) that generates oxygen atoms by electron impact dissociation of oxygen molecules, a dissociated oxygen atom, oxygen molecules, and a third body. It is generated by collision reaction (ozone generation reaction). The collisional dissociation reaction is completed in several ns to several tens of ns, and the three-body collision reaction is completed in several tens of μs when oxygen is used as a source gas, for example. Therefore, the pulse high voltage to be applied has a short rise time and a pulse voltage having a large pulse wave front value of 30 contributes to the collisional dissociation reaction, and the shorter the pulse wave tail length 34 and the pulse full width 33, the more energy is applied to neutral particles and ions. Since energy can be supplied only to electrons without giving them, the efficiency of ozone generation is improved. Here, the rise time is the time from the 10% point to the 90% point of the pulse peak value, and the pulse wave tail length is the time from the 100% point to the 0% point of the pulse peak value. The pulse width is the time from the start point (0% point) to the end point (0% point) of the pulse.
In the case of using a bipolar high pulse voltage, unlike the unipolar pulse high voltage, ions accumulated in the high voltage electrode 14 and the low voltage electrode 15 when the polarity of the voltage is reversed are the high voltage electrode and Since it moves toward the electrode facing the low-voltage electrode, the influence on the discharge formation by the charged particles on the electrode surface can be minimized. The source gas 12 may be any gas containing oxygen, such as air or oxygen, and oxygen is preferably used in order to efficiently generate active oxygen species and radical species. For the purpose of efficiently contributing highly reactive OH radicals to the treatment reaction, the raw material gas may contain water in proportion to mist water (H 2 O) or saturated water vapor. Further, the processing chamber 11 may be disposed in the reactor 10, and the object to be processed may be introduced into the reactor 10 in the form of mist simultaneously with the raw material gas.
Note that the present invention is not limited to the generation of reactive gases including active oxygen species and radical species described in the above-described embodiments. For example, for the treatment of harmful substances such as exhaust gas (NO decomposition) and dioxins. Reactors used, oxidation treatment steps in semiconductor processes, surface treatment treatments, sterilization treatments used in food processing, hospitals, etc. Of course, various changes can be made.
[0006]
【Effect of the invention】
As described above, the reactive gas generation method and apparatus of the present invention have the following effects.
(1) The high voltage electrode and the low voltage electrode are arranged in the vicinity of the reactive gas extraction part inside the reactor through a predetermined gap length so that the pressure in the discharge space is higher than the atmospheric pressure outside the extraction part. Since the reactive gas generated from the low-temperature plasma generated by the application of pulse high voltage is extracted from the extraction part, high-density reactive gas can be supplied and the post-processing part of the extraction part is processed. The reaction time with the object can be shortened, and efficient processing can be performed.
(2) Since the take-out part of the reactor has a nozzle shape, it is possible to maintain a stable pressure, and to obtain a high dissolution efficiency of the reactive gas into the object to be processed and to perform partial local processing.
(3) Since a high voltage pulse voltage with a steep rise is used, energy loss for accelerating gas molecules and various ions can be suppressed even under high pressure, and only electrons can be accelerated to increase electron energy. It is possible to improve the stability of generation of high-density low-temperature plasma. Further, since a streamer discharge is formed under a high pressure, it is possible to increase the discharge volume, and the discharge space utilization rate can be increased, so that the electric power injected between the electrodes can be used effectively.
(4) Since the surface of the electrode is uneven and an uneven electric field can be formed, stable low-temperature plasma can be easily formed even in a high-density state of gas.
(5) Since the electrode surface is covered with a dielectric, electrode deterioration due to sputtering, etc. does not occur, the life of the electrode can be extended, maintainability is improved, and a clean reactive gas free of discharge debris is generated. can do.
(6) Since the source gas and the reactive gas are specified, the active oxygen species having a higher reactivity than ozone can be used effectively.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a gas generator showing a first embodiment of the present invention.
FIG. 2 is a sectional view of a gas generator showing a second embodiment of the present invention.
FIG. 3 is a cross-sectional view of a gas generator showing a third embodiment of the present invention.
FIG. 4 is a sectional view of a gas generator showing a fourth embodiment of the present invention.
FIG. 5 is a sectional view of a gas generator showing a fifth embodiment of the present invention.
FIG. 6 is a sectional view of a gas generator showing a sixth embodiment of the present invention.
FIG. 7 is a sectional view of a gas generator showing a seventh embodiment of the present invention.
FIG. 8 is an explanatory diagram of a pulse high voltage to be applied.
FIG. 9 is a cross-sectional view showing a processing apparatus using a conventional reactive gas.
FIG. 10 is a sectional view showing another conventional reactive gas generator.
[Explanation of symbols]
10 reactor
11 treatment room
12 Raw material gas
13 Reactive gas
14 High voltage electrode
15 Low voltage electrode
16a, 16b dielectric
17 Low temperature plasma
18 Pulse power supply
19 Introduction
20 Extraction department
21 Nozzle
30 Pulse crest value
31 Rise time
32 Voltage rise speed
33 full pulse width
34 Pulse wave tail length
40 Ozone contact tank
41 Inflow pipe
42 Ozone gas injection part
43 Ozone generator
44 Water to be treated
45 Ozone gas introduction pipe
46 Exhaust ozone gas
47 High voltage power supply
48 Hollow fiber membrane

Claims (1)

A pulse power supply for generating a pulse high voltage having a voltage waveform with a steep rise ; and
The introduction of the raw material gas composed of oxygen or air,
A high voltage electrode and a low voltage electrode are opposed to each other through a predetermined discharge space, and the pulse high voltage is applied between the high voltage electrode and the low voltage electrode to form a streamer discharge in the discharge space. To generate a reactive gas containing radical species from the source gas by low-temperature plasma ,
A nozzle portion having a smaller cross-sectional area than the introduction portion, and an extraction portion for taking out the reactive gas from the reactor through the nozzle portion,
The source gas is introduced so that the pressure in the discharge space is higher than the pressure in the vicinity of atmospheric pressure , and the reactive gas is ejected from the nozzle portion at a high speed. Reactive gas generator.

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